Mucosal acid challenge activates nitrergic neurons in myenteric plexus of rat stomach

We tested the hypothesis that intrinsic neurons of the rat gastric myenteri c plexus can be activated by an acid (HCl) challenge of the mucosa. Activat ed neurons were visualized by immunohistochemical detection of c-Fos, a mar ker for neuronal excitation. The neurochemical identity of the neurons acti vated by the HCl challenge was determined by colocalizing c-Fos with a mark er for excitatory pathways, choline acetyltransferase (ChAT), and a marker for inhibitory pathways, nitric oxide synthase (NOS). Two hours after intra gastric administration of HCl or saline, stomachs were removed and immunofl uorescence triple labeling of myenteric neurons was carried out on whole mo unt preparations. Treatment with 0.35, 0.5, and 0.7 M HCl induced c-Fos in 8%, 56%, and 64%, respectively, of NOS-positive but not ChAT-positive neuro ns. c-Fos was also seen in glial cells of HCl-treated rats, whereas in sali ne-treated animals c-Fos was absent from the myenteric plexus. HCl treatmen t did not change the proportion of ChAT- and NOS-immunoreactive neurons in the myenteric ganglia. It is concluded that gastric acid challenge concentr ation-dependently stimulates a subpopulation of nitrergic, but not choliner gic, myenteric plexus neurons, which may play a role in muscle relaxation, vasodilatation, and/or secretion.